The present invention is related to an apparatus and a method for checking the alignment of laser beams on a diagnostic and/or therapeutic machine, the laser beams having the purpose to indicate a treatment position in relation to a therapeutic beam.
In radiation therapy, different diagnostic imaging methods are used in order to examine a patient in more detail. In particular, imaging methods are applied when there is a suspicion of a tumour disease, in order to represent location, size and position of the tumour in the patient's body in an image. For later irradiation of the tumour, a therapeutic device is used at a later point of time, which makes transfer of the diagnostic results to the therapeutic device necessary. When the location of the tumour is determined in the imaging process, it is necessary that at a later point in time, the patient should be aligned in relation to the therapeutic machine such that the therapeutic beam runs through the tumour. With a movable therapeutic beam, which impinges from different directions onto the region to be treated, it has to be taken care for the correct alignment of the patient that the isocentre of the therapeutic beam is located in the predetermined position. In a diagnostic machine, there is no machine-determined isocentre, but another mechanical reference point depending on the type of the machine, a so-called virtual isocentre. In a computer tomograph for instance, the virtual isocentre is defined on the rotational axis. In the following text, it is not distinguished between the isocentre of the therapeutic machine and the virtual isocentre of the diagnostic machine.
In order to bring the patient on the machine into a predetermined position, so that the tissue region to be treated is aligned accurately in relation to the therapeutic beam, markers are applied on the patient's skin in the diagnostic procedure. The locations for the markers are projected onto the patient's skin by lasers on the machine which executes the diagnostic procedure, for instance. The markers can be transferred to the patient's skin with a pencil, for instance. Also, it is possible to stick markers on the skin. For instance, the laser beams can be directed to a point which is envisioned as the future isocentre. When the patient is on the therapeutic machine, some days later, for instance, he/she is aligned by means of the markers on the therapeutic machine into a position allowing a determination of the treatment region. In order to perform accurate alignment of the patient, laser beams are projected onto the patient's skin again in an accurately defined way on the therapeutic machine, too. When the applied markers are coincident with the laser beams projected onto the skin, the patient is in the defined position again, so that size, location and alignment of the tissue region to be treated is accurately accomplished for the control of the therapeutic machine by means of the diagnostic data. When aligning the patient, the patient can be aligned again to the isocentre of the therapeutic beam on the therapeutic machine too, when the laser beams on the diagnostic machine are directed towards the envisioned isocentre.
The present invention is based on the objective to check on a therapeutic machine whether the laser beams for marking are correctly aligned in relation to the therapeutic beam.